In typical commercial electrographic reproduction apparatus (copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
One type of fuser assembly, utilized in typical reproduction apparatus, includes at least one heated roller and at least one pressure roller in nip relation with the heated roller. The fuser assembly rollers are rotated to transport a receiver member, bearing a marking particle image, through the nip between the rollers. The pigmented marking particles of the transferred image on the surface of the receiver member soften and become tacky in the heat. Under the pressure, the softened tacky marking particles attach to each other and are partially imbibed into the interstices of the fibers at the surface of the receiver member. Accordingly, upon cooling, the marking particle image is permanently fixed to the receiver member.
When the fuser assemblies include an external heater mechanism, a plurality of heater rollers are in contact with the external surface of a fuser roller. The rollers are subject to high loads and high wear of the surface coating. The ideal coating for the rollers would provide low surface energy so as not to attract and retain marking particles while, at the same time, being very resistant to wear in order to provide for long roller life. However, low surface energy coatings are not generally wear resistant in such application. In prior externally heated fuser assemblies, a long-life coating was used, but the fuser assemblies experienced many failures due to contamination. The heater rollers attracted marking particles, became contaminated and subsequently contaminated the fuser rollers. Subsequently, a low surface energy Teflon-type coating was tried, but these rollers also failed early in life when the coating wore off.
Further, with fuser assemblies of the above described type, it has been found that there is a tendency of a portion of the marking particles in an image to adhere to the pressure roller rather than remaining with the receiver member during the fusing operation. This is referred to as image offset. Thereafter the offset marking particles can transfer back to subsequent receiver members being fused to form undesirable image artifacts such as ghost images for example. Also, the offset marking particles may transfer to the fuser roller when no receiver member is present therebetween and then to the back side of subsequent receiver members to form undesirable marks thereon. In order to minimize this image offset effect, an offset preventing oil is applied to the rollers of the fuser assembly. The offset preventing oil has a viscosity which lowers the surface energy of the rollers and makes it less likely that marking particles will adhere thereto.
Since the offset preventing oil is not one hundred percent efficient in preventing image offset, and because the offset preventing oil itself can cause some image artifact problems during fusing, it has been found desirable to provide a mechanism for cleaning the fuser rollers of residual marking particles and excess offset preventing oil. One general type of cleaning mechanism used in reproduction apparatus includes a web cleaner. For example a typical web cleaner is shown in U.S. Pat. No. 4,853,741, issued Aug. 1, 1989, in the name of Ku, for cleaning photoconductive webs. The web cleaner has a roll of cloth material that runs from a supply roll to a take-up roll and is in contact with the surface to be cleaned (e.g., photoconductive web, fuser roller or pressure roller of a fuser assembly, or a transfer roller). The web material is, for example, a thin Nomex web material that is pressed against the heater rollers and wipes any marking particle accumulation from the heater rollers. After a predetermined number of reproductions have been made, the cloth material web is advanced a few degrees to the take-up roll to provide a clean web surface in contact with the surface to be cleaned.
Most web cleaners are rigidly mounted in a frame or slide, which tends to be over-constrained and results in uneven forces along the length. To overcome the over-constrained condition, tight tolerances or non-rigid frames are often employed. However, a non-rigid frame can twist and cause the web to have poor take-up (wrapping on a reel or spool). When the frame is non-rigid the spools may not be parallel which causes the web to track over to the side and eventually bind on the frame. Accordingly it has been found that there is some difficulty in maintaining effective cleaning contact between the cleaning web and the fuser heater rollers.